There are a great many situations in which it is necessary to determine the relative position or location of an object or feature, and/or in which information pertaining to relative position or location must be displayed in other than a purely numerical form in order to be meaningful or useful. Navigation is one field in which the ability to determine the display accurately relative positions is of critical importance, but for which the ability has heretofore been only partially attained. Although there are occasions, such as, for example, when a marine vessel is traversing the high seas, when navigation can be a comparatively leisurely process, since only a few navigational observations are required at relatively long intervals, and errors in position can usually be detected and corrected before danger threatens, the situation is drastically different in "pilot waters", or their land, air or space equivalent, where the danger of running afoul of obstructions is often imminent, frequent changes of course and speed are common, and the proximity of other vessels increases the possibility of collisions and restricts movement. In this type of situation, frequent, or even continuous, positioning with respect to charted features is necessary. Except for special circumstances, such as where a vessel is proceeding along a range, this positioning normally must be effected by constructing a plot on a chart based upon accurate navigational observations of charted features.
In pilot waters, or their equivalent, the speed and accuracy with which the necessary observations are made, the necessary calculations are performed, and the resulting information is plotted can mean the difference between safety and disaster. In recognition of this fact, much effort has been devoted in the prior art to the development of more precise and reliable navigational aids with which to obtain the raw data on relative position, of more efficient and powerful position-determining computers with which to convert the raw data into readily plotted information, and of faster, more flexible, and more accurate automated plotters with which to construct the plot.
However, conventional navigation systems which do not employ geometrical principles, whether they utilize simple mechanical calculators or complex electronic computers, have in general been characterized by the need for input data pertaining to the distance of the vessel from selected reference points and/or to the bearing of the vessel relative to selected reference points as defined with respect to an external frame of reference. As a consequence, complex, expensive, and delicate direction and distance finding equipment has been required, the high cost and fragility of which have discouraged more widespread use of such navigation systems. Further, applicant is aware of only one position-determining technique, described in Bowditch's The American Practical Navigator at Sections 1102-1103, wherein the distance of the vessel from selected reference points need not be known, and bearing information which is not referenced to an external coordinate system is used. However, this method, which is based on the geometrical principle that for any pair of observed points there is only one circle (the circle of equal angles) which passes through the two points and the observer's position, requires either the use of a special three-arm protractor or the actual construction of circles of equal angles. Such geometric constructions are laborious, error-prone, and time-consuming, if done manually, and most difficult and cumbersome to implement in an automated plotter.
Accordingly, it is an object of the present invention to provide a navigation system which automatically calculates and plots a vessel's position without the need either for measurement of the distance of the vessel with respect to any reference point, or for observation of reference points which are related to an external coordinate system.
It is another object of the present invention to provide a navigation system wherein the chart on which the vessel position is plotted itself serves as a data base from which data necessary to determine vessel position is derived.
It is an additional object of the present invention to provide an integrated position-determining and plotting navigation system wherein the chart on which the vessel position is plotted need not be aligned with any predetermined frame of reference associated with the plotter and neither the plotter nor the chart need be aligned with a predetermined frame of reference external to the navigation system, such as magnetic north.
It is a still further object of the present invention to provide a navigation system which can mathematically determine a vessel's position based solely on knowledge of the included angles defined by an observation point and three non-colinear reference points, and of the distance between the three reference points.
It is a further object of the present invention to provide a navigation system of high accuracy which nonetheless can utilize the simplest aids to navigation to obtain the requisite observations of reference points.
It is yet another aspect of the present invention to provide a low cost navigation system of modular design which is readily transportable, easily adapted to existing aids to navigation, and easily expanded in capability.
It is an additional object of the invention to provide position determining and position plotting apparatus and methods which have general utility, and which are compatible with existing position determining/plotting methods.